koobas.hobune.stream
How do you make a particle effect always emit upwards?
I have a particle effect on items that I want to always be going upwards, but I also have rigidbody physics on the items so they can be moved around. So if the item is flipped upside down, currently the particles will emit downwards since they are attached to the object. How can I make it to that the particles always flow in a single world relative direction, but still emit from the rotating box?
The main idea is to change the speed to World, instead of local. Local changes as we spin. World Y is always straight up.
The default particle system is moving because of two things. In the 1st section "Start Speed," then down under Shape it has "Cone" and 25 degrees selected. In theory, all you have to do is change Cone from Local to World -- but there's no setting for that (the top setting SimulationSpace->World/Local won't do it -- that says whether spawned particles track the emitter as it moves.)
So, we can't use Shape setting. If you check off Shape, it just blasts the particles local forward (+z,) so you also have to also set StartSpeed to 0. Now, we have to find something that will allow us to set a World speed.
If you open the "Velocity over Lifetime" section, you'll finally see it has an option, "Space", for local/world. so check the Velocity bubble, and change to World. Now we can set Y to +3 (for example) and have the particles always go up, no matter how we spin.
That just looks like a thin stream of smoke. To get the cone back, check the downArrow on the right side of the Velocity box and select "random between 2 constants" (could also use curves, but more work to set them.) Try Y from 4 to 6 (always up, but a little random) and x and z each from -1 to 1 (they go left or right, front or back.) If you want the cone angle, you have to compute it in your head -- for example, to get 45 degrees, make sure the up and sideways max speed are the same.
FYI, those settings are what the old particle system presented. The new one buries all those options and added Shape to auto-set the most common ways.
You can just change the Gravity option to negative and play around until it fits your needs.
